Circuit breaker



R. E. FRINK CIRCUIT BREAKER Jan. 8, 1963 3 Sheets-Sheet 2 Filed July l, 1959 Ils/Ll S R. E. FRINK CIRCUIT BREAKER Jan. 8, 1963 3 Sheets-Sheet v5 Filed July l, 1959 United States Patent C 3,072,764y CIRCUIT BREAKER f Russell E. Frink, Forest Hills, Pa., assigner to Westinghouse Electric Corporation, East Pittsburgh, Pa., a cerporation of Pennsylvania Filed July 1, 1959, Ser. No. 824,358 13 Ciaims. (Cl. 20G-106) This invention relates, generally, to circuit breakers' In some circuit breakers, rebound is controlled by a piston and cylinder arrangement which drives air through a very `small orifice, thereby decelerating the speed of the moving contact structure before it reaches its full open circuit position. Manufacturing of such a piston and cylinder arrangement requires close tolerance machinery, and thepiston must beiitted with rings which make the Idevice relatively expensive. The device also takes up considerable spaceand cannot-be adapted to some circuit breakers of a compact design. Furthermore, thearc eX- tinguishing capacityof such. a circuit breaker is lowered because the movable contact structure does not move at high speed to its fullopen circuit position.

Accordingly, an object of the invention is to provide au circuit breaker having a movable contact structure, movable athigh speed, with means for preventing rebound of the moving contact structure.

Another object of the invention'is to provide a circuit breaker having a movable Contact structure, movable at high speed to its full open circuit position, with means for preventing rebound of the contact structure when it is suddenly stopped in its opening movement.

A further object is to provide a circuit breaker with latching means, for'preventing rebound of the moving contact structure, which is dependable, inexpensive, easy to install and which takes up little space within the circuit breaker.

A still further object is to provide. a circuit breaker with latching means, for preventing rebound of the moving contact structure, which cannot interfere with the opening and closingV operation of the breaker. n

Another object is to provide, in a trip-free circuit breaker, an anti-rebound latch that prevents rebound of the moving contact structure during an opening operation, which latch is moved to an inoperative position when the trip-free linkages are reset for a subsequent closing operation.

Another object is to provide an anti-rebound latch for a circuitbreaker which latch is operative only at a time when ther closing coil. of the circuit breaker cannot be energized.

Another object is toprovide a spring-biased latching means, for preventing rebound of the moving contact structure of a circuit breaker, which will not interfere with the operation ofthe circuit' breaker in caseof failure of thespring.v

Inv accordance with one embodiment of my invention, alcircuit breaker is providedwith an anti-rebound latchingY member that temporarily latches the lever structure of the operatingmechanism during an opening operation. This arrests rebound of the movable contact structure from its open circuit position. The anti-rebound latch* ingmember is spring biased towards its latching position. 'This member is held in an inoperative position against the bias ofsaid spring bythe operating mechanism when the circuitbreaker is inthe open. and closed circuit positions.

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The invention both as to structure and operation t0- gether with additional objects and advantages thereof, will be best understood from the followingv detailed description thereof, when read' in conjunction with the aC- co'rnpanying drawings, in which:

FIGURE l is a view, partly in side elevation `and part-V ly in section, of a circuit breaker embodying the principles of the invention, the anti-rebound latch being omitted for the purpose of clarity;

FG. 2 is an enlarged' view, in side elevation, of a portion of' the circuit breaker showing the position of the anti-rebound latching mechanism of this invention when the contact structure of the circuit breaker is in the closed circuit position, some of the circuit breaker operating mechanism which is disposed within a frame being shown' in dotted lines;

FIG.' 3 is a view, similar to FIG. 2, showing the momentary position of the parts at the instant when the re; bound of the moving contact structure has been arrested during an opening operation;

FIG. 4 is a view, similar to FIG. 2, showing the position ofthe parts when the contact structure of the circuit breaker is in the open-circuit position, andv FIG. 5 is an enlarged View, in end elevation, of the anti-rebound latching mechanism in theV posi-tion shown in FIG. 4.

Referring to FIG. l of the drawings, the circuit breaker shown therein comprises, generally, 'a pluralityY of pole units (only one lbeing shown) mounted ona base structure indicated generally at'11. The pole unit comprises a channel-shaped frame 13 of' molded insulating'material rigidly supportedon the base structure 11 by means of a bracket 15 secured to the base structure 11 by means of bolts 17, the frame 13V being secured to the bracket by bolts 19 (only one 'being shown). The front of the frame 13l is secured, by bolts 21, to a bracket 23 which is securedr to the base structure 11 by bolts 25.

Supported in a rear'wall 27V of the insulating frame 13 are an upper terminal stud 31 and a lower terminal stud 33. The studs 31 and 33 extend through suitable openings in the rear wall 27 of the' frame 13 and have Contact blo-cks or feet 35 and 37, respectively, suitably secured to their inner ends.

The upper block 35 supports a stationary contact'struc# ture indicated generally at 39.` A movable switch member 41 comprising a pair of spaced arms' (only one being shown) is pivotally supported by avpin 43 on the lower contact foot 37. A movable contact' structure indicated generally at 45, is mounted between the arms of the movable member 41 for movement into and out of engagement with the stationary contact structure 39. The details of the contact structureare fully disclosed in a patent'to Dickinson et al., Patent No. 2,866,043, assigned to the assignee of the present invention. For this reason, only a brief description of the contact structure is included herein. y The stationary contact structure 39 comprises a main stationary Contact 47 biased by a spring 49'for contact follow, and a stationary arcing Contact 51. Thefmovable contact structure comprises a main movable contact 53 rigidly supported between the contactarms 41, and a movable arcingcontact 55 biased by a spring 57 for contact follow.

The movable switch member. 41y is connected by an insulating rod 56 to a lever structure which. is part of the breaker operating mechanism mounted in the'base structure 11. This llever, structure comprises an'operating lever 58 and an operating rod-62 which isrotatably supported in the operating lever. The insulating rod` 56 is pivotally connected by a pin 60 to the switch arms 41, and by the operating rod 62 to the operating lever 58; The

operating lever 58 is in the base 11.

All of the poles of the breaker are connected to the common operating rod 62, and they are all, therefore, operated by the one operating lever 58.

An operating linkage, comprising toggle links 59, 61 and 63, is provided to releasably hold the operating lever 58 and, consequently, the movable contact structure in the closed position, and to operate the movable contact structure to open and closed positions. The toggle link 59 is pivotally connected by means of a pivot pin 65 to the operating lever 58, and the toggle link 63 is pivoted on a xed pivot 67 supported on a housing 66 that is mounted on the base structure 11. The toggle link 61 is pivotally connected to the links 59 and 63 by knee pivot pins 69 and 71, respectively.

The linkages 59, 61 and 63 comprise two toggles, one of which 59, 61 may be designated as the tripping toggle and the other 61, 63 as the closing toggle. The tripping toggle 59, 61 is normally slightly underset above a line drawn through the center of the pivot pins 65, 71, and the closing toggle 61, 63 is normally underset below a line drawn through the centers of the pivot pins 67, 69. The closing toggle 61, 63 is normally prevented from col lapsing downward by a support member 73 that is pivoted on a pin 75 supported in the housing 66, and that has a shoulder portion engaging under the knee pivot pin 71. The tripping toggle 59, 61 is normally prevented from collapsing by means of a main latch member 77 that is pivoted on a pin 78 in the base 11. A link 79 is connected to a pivot pin 80 Which is attached to the main latch member 77. The link 79 is connected to the knee pin 69, thereby connecting the main latch member 77 to the tripping toggle 59, 61.

The main latch member 77 is held in latching position by an intermediate latch lever 81 that is pivoted on the pin 75 and biased (by means not shown) to latching position. The intermediate latch lever carries at its upper end a latch roller 83 engaging a latch nose 84 on the main latch 77, and at its lower end the intermediate latch lever has a latching portion 85 normally engaging a latch roller 87 on a trip member 89 that is pivoted on a pin 91 in the frame 66. The trip member 89 is biased by spring means (not shown) to the latching position. A bracket 97 that is secured to the trip member 89, has a screw 99 adjustably mounted thereon for cooperating with a trip device 100 shown in the form of a tripping electromagnet.

The circuit breaker is tripped open by operation of the tripping magnet 100 whose armature 101, upon energization of the magnet by a tripping impulse, engages the screw 99 and rotates the trip member 89 counterclockwise, causing the latch roller 87 to release the intermediate latch 81. The latching engagement of the main latch 77 with the latch roller 83 is of the slip-olf type, and as soon as the intermediate latch 81 is released it is moved to an unlatching position by the upward force applied to the main latch 77 through the link 79. The tripping toggle 59, 61 immediately collapses upwardly, permitting counterclockwise movement of the operating lever 58 and opening movement of the movable contact structure. During the collapse of the tripping toggle 59, 61, a por tion of the toggle link 61 engages and actuates the support member 73, against the bias of a spring 110, to a non-supporting position, thereby freeing the closing toggle 61, 63. The closing toggle thereupon collapses downward under the Weight of armature 112, and during its collapse resets and relatches the tripping toggle 59, 61. The circuit breaker is closed by energization of a closing solenoid 111, the armature 112 of which is connected by means of a rod 113 to the knee pin 71 of the closing toggle. When a solenoid coil 114 is energized, which may be effected either manually or automatically by closing a suitable switch (not shown), the armature 112 and rod 113 are thrust upwardly straightening the closing toggle 61, 63. Since the tripping toggle 59, 61 is pivotally supported on a pin 64 now held in thrust transmitting position, the operating lever 58 is moved clockwise to close the breaker.

A latch check switch 102 is mounted on the base 11 below the bracket 97. This switch has a movable push button 104 which is depressed to a closed position by a screw 106 mounted on the bracket 97 when the circuit `breaker is in the closed and open circuit positions (FIGS. 2 and 4). The latch check switch 102 is connected in series with the closing solenoid coil 114. The closing coil 114, therefore, cannot be energized when the latch check switch 102 is open. When the circuit breaker is tripped, a cam surface 108 on the intermediate latch 81, rides over the latch roller 87 of the trip member 89 maintaining the trip member 89 in the counterclockwise position shown in FIG. 3. In this position, the push button 104 is no longer depressed by the screw 106, and the latch check switch 102 is open. When the linkage resets, the cam surface 108 rides oli of the latch roller 87, and the trip member 89 rotates clockwise closing the latch check switch 102 (FIG. 4).

The latch check switch 102 remains closed at all times except from the instant the circuit breaker is tripped until the linkage has completely reset. During this short period of time, the latch check switch 102 is open and prevents energization of the closing solenoid coil 114.

Upon opening of the movable contact structure, a gasblast device or puffer, indicated generally at 115, provides a blast of air between the separating contacts. The putter comprises, generally, a diaphragm 121 and a chamber 117 that is dened by a cup-shaped base casting 119 extending across the three poles of the breaker and integral with and supported by the bracket 1S which supports the frame 13. The edges of the diaphragm 121 are secured to flanges 123 on the casting 119 by bolts 127. The center portionv of the diaphragm 121 is clamped between two clamping members 129 and 131 which are secured on one end of a rod 133. the other end of which is pivotally connected by a pivot pin to the operating lever 58.

Connected to the upper portion of the casting 119 is a pipe 137 which at its upper end is provided with a suitable nozzle 139 for delivering a blast of air to the contacts upon opening movement of the movable contact structure. The clamp members 129 and 131 are secured to the rod 133 on opposite sides of the diaphragm 121 by nuts 141 and 143 which are threaded 0n the rod. A compression spring 145 compressed between the casting 119 and a washer 147 on the rod 133 biases the rod and the operating lever 58 in contact opening direction.

Referring now to FIGS. 25, in order to prevent rebounding of the moving contact structure when it is stopped during an opening operation, an anti-rebound latching member 149 is provided. The latching member 149, which has a hooked catching surface 150, is pivotally mounted at the outside of the housing 66 on the pivot pin 67 which extends a short distance out through a side of the housing. The pivot pin 67 is supported at its outer end in a hole in a mounting bracket 151 which bracket is bolted to the base of the housing 66 by bolts 153. Washers or spacer elements 155 and 157 are provided at each side of the anti-rebound latching member 149 restricting this member from lateral movement between the mounting bracket 151 and a circular abutment 158 which is integral with the housing 66.

The anti-rebound latching member 149 is biased in a counterclockwise direction about the pivot pin 67 by a spring 159, one end of which is hooked into a hole 161 in the latching member 149, the other end being hooked into a hole 163 in an L-shaped spring mounting bracket 165. The spring mounting bracket 165 is secured to the housing 66 by bolts 167.

A Contact pin 169 is welded to the anti-rebound latch.. ing member 149 and protrudes through a hole 171 in theside of the housing 66. A small cylindrical abutment 173 is eccentrically disposed at the free end of pin 169.

5. Asis shown in FIG. 2 when the circuit interrupter is closed, the spring 159 is held under expanded tension because the operating rod 62 engages the free end ofthe anti-rebound latching member 149, preventing rotation of this member in a counterclockwise direction about pin 67. The closing toggle 61, 63 is prevented from collapsing downward by the support member 73 (FIG. 1).

When the circuit interrupter is tripped open, the operating lever 5S, under the force of Compression spring 145, pivots counterelockwise about the pin 64 until the surface 103 of the operating lever 53 strikes the abutment 165 of the housing 66, at which instant the operating lever starts to rebound towardsits closed circuit position. Only a very slight rebound is permitted, however, because when the operating rod. 62 clearsy the endof the hooked catching surfacey G of the anti-rebound latching member 149, the spring 159 retracts moving the member 11i@ in a counterclockwise. direction about pivot pin 67`, and the hooked catching surface 15) of member 149 engages the operating rod 62, preventing further rebound of the operating lever 5S. This momentary position of the parts is shownin FIG. 3i.

After the rebound of the operating lever Sis arrested, thislever, under theweight of the-movable contact structure, settles back to its full open position with-its surface 103 resting on the abutment 105 of the casing `66,- thus disengaging the hooked surface 150 of the. anti-rebound latching member 149 from the operating rod 62 to allow a clockwise movement of this member which movement will be described later. v i

During the opening operation, when the tripping toggle 59, 61 collapses upwardly, the toggle link 61 engages and actuates the support member 73 (FIG. 1) against the bias of spring 11G to a non-supporting position, thereby freeing the closing toggle 61, 63 (FlG. 3f). The position of the linkage in FIG; 3V is only momentary, because at this instant,y the closingl toggle 61', 63, being no longer supported by the support member 73 (FIG. l) is about to collapsek downwardly under the weight' of the armature 112'(FG. 1)'.

As the closing-toggle 61, 63 collapses downwardly, the toggle link 63 `engagesthe cylindrical abutment 173 on the free end of contact pin 169 and moves the antirebound latching member 149 ina clockwise direction about pivot pin 67 to its unlatched open-circuit position (FIGS. 4 and^` 5); In this position thefspring 159 is again held under expanded tension.

The'toggies 61, 63 and 59, 61 off the operating mechanism are trip-free. During an opening operation, the contacts cannot be closed until after the armature 112 drops resetting the toggles 61, 63 and 59, 61 asshown in FIG. 4.

The parts will remain in this positionuntil the circuit interrupter is closedby energization of the closing solenoid 111 (FIG. l) at which-time the armature 112 and rod 113y are thrust upwardly, straightening, the closing toggle 61, 63 and moving the operating lever 5S clockwise to its closed circuit position (FlGS. 1 and 2). Because the toggle link 63 is moved out of engagement with the cylindrical abutment 173 of contact pin 169, the

, anti-rebound latching member 149 is free to move counterclockwiseunderpthe retracting force of spring 159 until its Vfree'end engagespthe operating rod 62(F1G; v2).

The parts are now in position for another anti-rebound opening operation.

rEhe anti-rebound latch 149 is operated toa latclling position only during the short periodv of time during a tripping or opening operation' before the linkageresets (Pi. 3); During kthis Vshort periodv of time, the latch check switch-102 is open-and the closing coil 114 cannot be energized. When the latch check switch 102 is closed allowing energization of theclosing coil 114`, the antirebound latch 149 is heldin inoperative positions (FlGS.

2'and'4`). Thev anti-rebound latch 149, therefore, cannot interfere with the normal operation of the circuit breaker.

6 If the spring 159' breaks, the anti-rebound latch 149` will drop clockwise until the pin 169 comes to rest on the lower inside rim of opening 171, and the circuit breaker.` will operate normallyk without anti-rebound means. Thus,` the anti-rebound. means isy of a fail-safe type.

'it will be seen that the invention provides a circuit.

breaker with anti-rebound means-which permits the movable contact structure to move at highspeed to its full open-circuit position and which cannot interfere withqtheopening or closing operations of the circuitl breaker.

While the invention has been disclosed in accordance with the provisions of the patent statutes, it is to be under.- stood that various changes in the structural details and arrangement of parts thereof may be made without departing from the spirit of the invention;

l claim as my` invention:

l. A circuit breaker having stationary contact means and movable contact means cooperating4 therewith to openand close saidbreaker, said movable contact means being movable at high speed to its full open-circuit position, means latching said movable contact means for. only a moment during an opening operation to prevent rebound of said movable contact structure from its opencircuit position, and means movingl said latching means out of latching position at the expiration of saidmornent 2. A circuit breaker comprising, in combination, -stationary contactv means, a movable contact structure havingY movable Contact means thereon for cooperating with said stationary contact means to open and close said breaker, an operating mechanism for moving said movable contact structure, latehing means temporarily co'- operating with said operating mechanism during an opening operation to arrest rebound of said movable contact structure from its open-circuit position, and means maintaining said latching means in an inoperative position when said operating mechanism is set for a closing operation.

3. In a circuit breaker having cooperating contacts, a movable contact structure movable to effect automatic opening, an'dclosing of said contacts, an operating mechanism for moving said movable contact structure, and anti-rebound latching means momentarily latching said operating mechanism during an opening operation immediately aftersaid contactV structure reaches its full opencircuit position. t

4. In a circuit breaker having relatively movable contacts, a movablecontact structure movable to eiect automatic opening and. closing ofsaid contacts, anV operating mechanism for moving said movable contact structure, said operating mechanism comprisinga trip-freeY linkage and a lever structure cooperating with said` trip-freelinkage during anopening and closing operation, anti-rebound means momentarily engaging saidlever structure to arrest rebound of said movable contact structure during the opening operation, said anti-rebound means being moved to an inoperative position when said trip-free linkage is reset fora subsequent closing operation.

5. A circuit breaker comprising stationary contact means and a movable contactl structurehaving movable conta-ct means thereon for cooperatingy withv said stationary contact means to open and close said circuit breaker, an operating mechanism forV moving said' movable contact structure, said operating mechanism comprising an operating linkage and a lever structure cooperating with said operating linkage during an opening, and closing operation, anti-rebound means momentarily engaging said lever structureto arrest rebound of said movable contact. structure duringthe opening operation, said anti-rebound meansbeing biased to aninoperative positionby saidA lever structure when said circuit. breaker is in the closed-circuit position, andk said anti-rebound means being biased to an inoperative position by said operating .linkage when-said circuit breaker is in the opencircuit position.

6. A circuit breaker comprising, in combination, stationary contact means, a movable contact structure, movable contact means carried by said movable contact structure for cooperating with said stationary contact means to Open and close said circuit breaker, an operating mechanism for moving said movable Contact structure, spring biased anti-rebound means cooperating with said operating mechanism during an opening operation to prevent rebound of said movable contact structure, and said anti-rebound means being held inoperatively by said operating mechanism against the bias of said spring when said circuit breaker is in the open and closed circuit positions.

7. A circuit breaker comprising, in combination, stationary contact means, a movable contact structure, movable contact means carried by said movable contact structure for cooperating with saidk stationary contact means to open and close said circuit breaker, an operating mechanism for moving said movable contact structure, a closing solenoid cooperable with said operating mechanism, said circuit breaker being closed by energization of said closing solenoid, anti-rebound means temporarily cooperating with said operating mechanism during an opening operation to prevent rebound of said movable contact structure, and means to prevent energization of said closing solenoid during an opening operation.

8. A circuit breaker comprising stationary contact means and a movable contact structure having movable contact means thereon for cooperating with said stationary contact means to open and close said circuit breaker, an operating mechanism for moving said movable contact structure, said operating mechanism comprising an operating linkage and a lever structure cooperable with said operating linkage during an opening and closing operation, a housing having a hole in one side thereof, said operating linkage being disposed substantially within said housing, anti-rebound means having a latching surface for momentarily engaging said lever structure during the opening operation, said anti-rebound means being disposed outside of said housing and having a contact member extending from one side thereof through said hole in said housing, and said operating linkage contacting said contact member to hold said anti-rebound means in an inoperative position When said circuit breaker is in an open-circuit position.

9. A multi-pole circuit breaker comprising, in combination, a plurality of stationary contact means, a movable contact structure comprising a plurality of movable contact means for cooperating with said stationary contact means to open and close said circuit breaker, said movable contact structure being movable at high speed to its full open-circuit position, means latching said movable contact structure for only a moment during an opening operation to prevent substantial rebound of said movable contact structure from its full open-circuit position, and means moving said latching means out of latching position at the expiration of said moment.

10. A multi-pole circuit breaker comprising, in combination, a plurality of stationary contact means, a plurality of movable contact structures having an operating rod attached thereto, said movable contact structures comprising a plurality of movable contact means for cooperating with said stationary contact means to open and close said circuit breaker, and an anti-rebound member having a hook-shaped surface thereon for momentarily catching said operating rod during an opening operation to prevent rebound of said movable Contact structures from the open-circuit position.

11. A multi-pole circuit breaker having a plurality of stationary contact means, a plurality of movable contact structures having an operating rod attached thereto, said movable contact structures comprising a plurality of movable contact means for cooperating with said stationary contact means to open and close said circuit breaker, and anti-rebound means engaging said operating rod during an opening operation immediately after said movable contact structures reach the full open-circuit position to arrest rebound of said movable contact structures, said anti-rebound means being biased to an inoperative position by said operating rod when said movable contact structures are in a closed-circuit position.

12. A multi-pole circuit breaker comprising, in combination, a plurality of stationary contact means, a plurality of movable contact structures having movable contact means thereon for cooperating with said stationary contact means to open and close said circuit breaker, an operating mechanism for moving said movable contact structures, said operating mechanism comprising an operating linkage and a lever structure coperating with said operating linkage during an opening and closing operation, a housing having a hole in one side thereof, said operating linkage being disposed substantially within said housing, a spring biased anti-rebound member for momentarily catching said lever stucture during an opening operation to prevent rebound of said movable contact structures, said anti-rebound member being pivotally supported outside of said housing and having a contact member extending from one side through said hole in said housing, said operating linkage contacting said contact member to hold said anti-rebound member in an inoperative position against the bias of said spring when said circuit breaker is in an open-circuit position, and said lever structure contacting said anti-rebound member to hold said anti-rebound member in an inoperative position against the bias of said spring when said circuit breaker is in a closed-circuit position.

13. A circuit breaker comprising stationary contact means and a movable contact structure having movable contact means thereon for cooperating with said stationary contact means to open and close said circuit breaker, an operating mechanism for moving said movable contact structure, said operating mechanism comprising an operating linkage and a lever structure cooperating with said operating linkage during an opening and closing operation, a housing having a hole in one side thereof, said operating linkage being disposed partially within said housing, anti-rebound means cooperating with said lever structure during an opening operation to prevent rebound of said movable contact structure, a spring biasing said anti-rebound means towards a latching position, said anti-rebound means being disposed outside of said housing and having a contact member extending from one side thereof through said hole in said housing, said operating linkage contacting said contact member to hold said anti-rebound means-in an inoperative position against the bias of said spring when said circuit breaker is in an opencircuit position, upon the breaking of said spring said latching member falling until said contact member rests on the lower inside rim of said hole in said housing, said hole being of such size that when said contact member rests on the inside rim of said hole said latching member is in an inoperative position where it cannot interfere `with the opening and closing operation of said circuit breaker.

References Cited in the tile of this patent UNITED STATES PATENTS 1,271,001 Zimmer July 2, 1918 1,732,750 Hodgkins Oct. 22, 1929 1,818,832 Walle Aug. 1l, 1931 2,195,818 Koppelmann et al. Apr. 2, `1940 2,298,143 May Oct. 6, 1942 2,343,255 Fisher Mar. 7, 1944 2,401,538 Anderson June 4, 1946 2,533,040 Betrak Dec. 5, 1950 2,748,215 Davis May 29, 1956 2,794,887 Noyes June 4, 1957 2,909,632 Pelenc Oct. 20, 1959 2,913,558 Bottonari Nov. 17, 1959 

4. IN A CIRCUIT BREAKER HAVING RELATIVELY MOVABLE CONTACTS, A MOVABLE CONTACT STRUCTURE MOVABLE TO EFFECT AUTOMATIC OPENING AND CLOSING OF SAID CONTACTS, AN OPERATING MECHANISM FOR MOVING SAID MOVABLE CONTACT STRUCTURE, SAID OPERATING MECHANISM COMPRISING A TRIP-FREE LINKAGE AND A LEVER STRUCTURE COOPERATING WITH SAID TRIP-FREE LINKAGE DURING AN OPENING AND CLOSING OPERATION, ANTI-REBOUND MEANS MOMENTARILY ENGAGING SAID LEVER STRUCTURE TO ARREST REBOUND OF SAID MOVABLE CONTACT STRUCTURE DURING THE OPENING OPERATION, SAID ANTI-REBOUND MEANS BEING MOVED TO AN INOPERATIVE POSITION WHEN SAID TRIP-FREE LINKAGE IS RESET FOR A SUBSEQUENT CLOSING OPERATION. 